<< So you think God had no laws before the Mosaic/Levitical laws and He has no laws today? >>
I don't know why you would come to that conclusion. The question requires speculation. Speculation is a great fertilizer for heresy.
<< What does He write on our hearts then? >>
You are asking for a subjective answer. The writing of the law on our hearts is a metaphor.
<< Melchizedek DIDN'T tithe,>>
How do you know that? There is no mention in scripture as to whether he did or did not.
<< Abraham tithed TO Melchizedek.>>
He gave him a tithe of the spoils of a military campaign. There is no evidence that Abraham tithed annually to Melchizedek. It does not provide support for the corrupted version of the tithe taught by many Christian churches today.
Abraham's tithe of the spoils (not of his total gain) relates to a single event and can not be employed to set a precedent for gentile believers some 2000 years later. Any generalization from that event is pure speculation. We do not build properly Christian doctrine on speculation. "Do not go beyond what is written." (1 Cor 4:6)
<< That Abraham already knew this was indicative of it being one of God's law for Abraham AND his descendants.>>
That is speculation. Paul's instructions were specific.
<< Do you only believe God all of a sudden decided that His people should have laws in a written form?>>
That is an astounding question. What do you think the Old Covenant was? It specifically established a covenant relationship with the people whom God had chosen as "his people."
It wasn't "all of a sudden" because God is not constrained by our experience of time. It was His eternal purpose to establish that covenant and the tithe is a part of that covenant.
<< Do you also want to do away with the 10 commandments that were the written foundation of the Mosaic law, or should they be filtered through the lens of the NC/NT?>>
Jesus gave the command to love one another. I can not love my neighbor by murdering him or stealing from him or giving false testimony about him or by laying with his wife.
The issue is whether you want to put people back under the Law of Moses.
<< Jesus said tithing was the right thing to do, and never said to stop doing it. >>
In what contest did He say that? He was speaking as a Jew to Jews under the law.
<<It's one a the few things He addressed in His earthly ministry and obviously for a good reason, just as He addressed the law of love.>>
Jesus spoke once about tithing in the Gospels. It is recorded by Matthew and Luke.
Mat 23:23
"Woe to you, scribes and Pharisees, hypocrites! for you tithe mint and dill and cummin, and have neglected the weightier matters of the law, justice and mercy and faith; these you ought to have done, without neglecting the others.
Luke 11:42
"But woe to you Pharisees! for you tithe mint and rue and every herb, and neglect justice and the love of God; these you ought to have done, without neglecting the others.
<< Please don't give me that crap that He was speaking under the OC/OT, because He wasn't, He was speaking as one who had been given ALL authority. >>
Crap?? The New Covenant had not yet been established.
When it was established, the apostles specifically stated that Gentiles were not required to be circumcised or keep the law of Moses. The tithe of which Jesus spoke when addressing the scribes and Pharisees was the tithe spelled out in the Law of Moses.
<< The minimum of TITHE would be a good place to start given it was one of the few OT practises Jesus applauded. >>
He did not "applaud" it. He used it as a point of departure to rebuke the scribes and Pharisees for their Hypocrisy of fastidiously keeping the letter of the law and then neglecting the important teaching of the law.
I would say that 10% is a good starting goal. On the other hand, if I could live on 10% of my income, I think it would be good to give the remaining 90% to the poor. In fact, just giving 105 in that circumstance and spending the rest on myself would, IMO, be sinful.
But I believe it is also sin for a pastor to tell poor people who are just scraping by that they are violating God's will if they don't give 10% of what they have to the church and then don't make sure they have enough to eat, clean water to drink, clean warm clothes to wear, etc. One pastor I know gave everyone in the church a booklet on tithing that said if you don't tithe you aren't saved. Now THAT is "crap."
<< let me remind you that as Jesus brought forward the law of love and self control, He also brought forward other laws that were designed to benefit us, and tithing is one of them. >>
No. He did not bring tithing forward as a law designed to benefit us. That is a fabrication.
<<To say that submitting to it, a law that existed before the written Mosaic/Levitical Law,>>
That, again is a false argument.(Logically, a "red Herring" fallacy) From the Bible, we do not know what, if any, laws existed before the Law of Moses. Extrapolation from the one recorded tithe of the spoils of war by Abraham to Melchizedek is pure speculation and not a valid basis by which to support a doctrine.
<< is not our responsibility under the NC is to say we are also not responsible to love our neighbours. Obviously this is not so, is it?>>
Obviously, that is illogical and not so. Jesus taught that we should not only love one another (friends and family, our community) but that we should love our enemies and despised people as well. The example of "neighbor" he gave was the Samaritan. Samaritans to the Jews in 1st century Judea were approximately equal to blacks in Montgomery Alabama in 1960.
<< Jesus didn't condemn those in Luke 21:1-4 that did tithe, He praised the women who put in much more than the minimum.>>
(1) The passage in Luke 21 refers to those who gave gifts, not tithes. Those are two different things. Don't conflate the two.
(2) He said they had given from their abundance. They gave their "spare change."
He said, concerning the wealthy who gave their "spare change" "
Thus, when you give alms, sound no trumpet before you, as the hypocrites do in the synagogues and in the streets, that they may be praised by men." (Mat 6:2)
<< Great example of giving till it hurts, also an example of how the minimum was NOT rejected.>>
No gift is rejected.
Telling poor people who lack the income to feed, clothe, and shelter their families that they must tithe or that if they don't tithe it's because they don't trust God is equivalent to the Pharisees binding "
heavy burdens, hard to bear, and lay them on men's shoulders; but they themselves will not move them with their finger." (Mat 23:4) Jesus told them to repent of go to hell.
Instead of speculating about what laws might have existed before the Law of Moses, talk to a single mother who just got laid off from her job. Tell her about how it's God's law that she give a tithe to the church from whatever little bit of money she manages to scrape together for herself and her children.